1. Field of the Invention
The present invention relates to a non-single-crystal semiconductor light emitting device which is produced through using a non-single-crystal semiconductor.
2. Description of the Prior Art
Conventionally known as a non-single-crystal semiconductor light emitting device is one that comprises a first electrode, a first non-single-crystal semiconductor layer of a first conductivity type, which is formed on the first electrode and makes ohmic contact therewith, an I-type non-single crystal semiconductor region formed on the first non-single-crystal semiconductor layer, a second non-single-crystal semiconductor layer of a second conductivity type reverse from the first conductivity type, which is formed on the I-type non-single-crystal semiconductor region, and a second electrode which is formed on the second non-single-crystal semiconductor layer and makes ohmic contact therewith. In this case, the non-single-crystal region is formed by a single non-single-crystal semiconductor layer.
With the light emitting device of such a construction, when connecting a DC bias source of a predetermined polarity between the first and second electrode, electrons (or holes) are injected into the non-single-crystal semiconductor region from the first electrode towards the second electrode, and holes (or electrons) are injected into the non-single-crystal semiconductor region from the second electrode towards the first electrode layer. The electrons (or holes) injected into the non-single-crystal semiconductor region from the first electrode flow towards the second electrode without being accumulated at the bottom of the conduction band (or valence band) of the single non-single-crystal semiconductor layer forming the non-single-crystal semiconductor region. Similarly, the holes (or electrons) injected into the non-single-crystal semiconductor region from the second electrode flow towards the first electrode layer without being accumulated at the bottom of the valence band (or conduction band) of the single non-single-crystal semiconductor layer forming the non-single-crystal semiconductor region. The electrons (or holes) thus flowing in the non-single-crystal semiconductor region from the first electrode towards the second one and the holes (or electrons) thus flowing from the second electrode towards the first one are recombined with each other in the non-single-crystal semiconductor region. As a result of this, light is obtained in the non-single-crystal semiconductor region, and this light is emitted as the output light from the non-single-crystal semiconductor light emitting device.
With the conventional non-single-crystal semiconductor light emitting device described above, those of the electrons (or holes) injected from the first electrode which do not recombine with the holes (or electrons) but reach the second electrode are nonnegligibly large in quantity, and those of the holes (or electrons) injected from the second electrode which do not recombine with the electrons (or holes) but reach the first electrode are also nonnegligibly large in amount. This stems from the construction of the device itself and imposes severe limitations on its light emitting efficiency.
Further, the prior art device has the defect that the light therefrom cannot be obtained as light close to white light even by a suitable selection of the energy band gap of the non-single-crystal semiconductor layer forming the non-single-crystal semiconductor region.